The present invention relates to non-streaking black color formulations for polycarbonate-siloxane resins and blends containing polycarbonate-siloxane resins. The present invention further relates to resins containing the non-streaking black color formulations.
Polycarbonate-siloxane copolymers and blends contain two immiscible phases. When the median siloxane domain size is greater than 100 nanometers, the matrix appears translucent or even opaque depending on part thickness, which creates several colorability problems. When the domains are of irregular shape, size corresponds to the largest dimension of the domain.
Domain sizes are characterized using microscopic techniques such as Scanning Electron Microscopy, Transmission Electron Microscopy. Typically, median size is determined from the distribution of the domain sizes measured according to the SEM or TEM techniques. Since the siloxane domains in these copolymers and blends are of a non-negligible size compared to the wavelengths of visible light, and with the refractive index of these domains being significantly different from the polycarbonate phase, a significant amount of light scattering occurs.
The result is a white xe2x80x9cmilkyxe2x80x9d appearance that makes high chroma colors, very low chroma colors and color depth very hard to obtain. In addition, local differences in particle size distribution of the siloxane domains in a molded part usually result in the appearance of visible defects referred to as streaking, flow-lines or knit-lines. The heterogeneous nature of the system also creates opportunities for the colorants to segregate, as they would have more affinity for one domain compared to the other.
As a result of the aforementioned factors, an aesthetically appealing jet-black color has never been achieved in a molded part from a polycarbonate-siloxane copolymers or blends composition with a median siloxane domain size greater than 100 nanometers.
It is well known to those skilled in the art that jet-black colored resins are usually obtained by addition of carbon black. Commercial jet-black color formulations in polycarbonate and polycarbonate blends typically contain between 0.2 and 0.5% of carbon black. However, such formulations cannot be incorporated into polycarbonate-siloxane copolymers and blends having a median siloxane domain size greater than 100 nanometers because streaks (also referred to as knit-lines or flow-lines) appear in the finished article made from the colored resin.
It would be desirable to provide a colorant composition providing low lightness and very low chroma polycarbonate-polysiloxane in copolymers and blends having a median siloxane domain size greater than 100 nanometers. It would further be desirable to provide a colorant composition providing jet black polycarbonate-polysiloxane copolymers and blends having a median siloxane domain size greater than 100 nanometers.